1. Field of the Invention
This invention is directed to a papermakers' press felt of the batt-on-mesh type having increased abrasion resistanoe, batt retention, and dimensional stability. More particularly, the invention is directed to the woven mesh base which comprises nylon yarn in the machine direction and nylon yarn encapsulated with ionomer resin in the cross-machine direction.
2. Description of the Prior Art
Press felts are commonly used for supporting and draining papermaking material during the papermaking process. In recent years, changes in the industry-wide practice of papermaking have placed greater demands upon the press felts. Primary among these changes are increased roll speed, greater use of conditioning equipment, and greater roll pressures. These same changes now require that the current papermakers' felt have a surface fine enough to produce a smooth finish, open enough to allow water to drain quickly, and resilient enough to quickly recover from repeated high nip pressures. Very importantly, these press felts must be constructed of materials which allow for improved batt retention, abrasion resistance, and dimensional stability.
Batt-on-mesh needled felts which consist of a batt of fibrous material needled to a woven mesh base are well known in the art and possess several characteristics required by the industry. The smooth surface and high drainage characteristics of these felts have been responsible for their extensive use throughout the papermaking industry.
However, these batt-on-mesh needled felts are not without their own problems. One problem is that the abrasive action of the press rolls causes the batt surface to shed fibers after a relatively short period of use. Another problem is that the increased use of the various types of conditioning equipment required to keep the felts clean also cause abrasion and fiber shedding. This has an adverse effect on the dimensional stability and the efficiency of current felts.
One effort to improve the abrasion resistance of the mesh base of a papermakers' felt is disclosed by Bond, U.S. Pat. No. 4,370,375. Bond provides a woven, heat set, papermakers' felt comprising machine and cross-machine direction thermoplastic filaments. At least 25% of the cross-machine direction filaments are oriented polyamide monofilaments having a diameter of about from 5 to 30 mils, these polyamide monofilaments including 3-10 weight percent, based on the total weight of the filament, of molybdenum disulfide. Among the disadvantages of the disclosure of Bond is that the molybdenum disulfide must be blended with the nylon prior to formation of the nylon fiber.
Prior art methods for improving the dimensional stability of the mesh base of papermakers' felts include forming the mesh with metal warps. This practice fell into disuse because the metal strands are subject to damage as a result of crinkling or creasing during shipping and installation. Additionally, such belts have low flexural fatigue resistance as compared to synthetic belts. Fleischer, U.S. Pat. No. 4,093,512, discloses a papermakers' mesh for use in papermaking machines comprising ultrahigh modulus, load-bearing yarn having a modulus of elasticity greater than 150 grams per denier in the machine direction. Included in the Fleischer disclosure is the concept of resin coating or wrapping and then resin coating the ultrahigh modulus yarns to improve their abrasion resistance and degradation resistance. Asbestos, nylon, and polyester are disclosed as contemplated wrapping materials; while nylon resins, water-based acrylics, phenolic resins, and amine resins are disclosed as suitable coating resins. The only fiber actually disclosed in the reference is a poly (para-phenylene terephthalamide).
Khan, U.S. Pat. No. 4,259,394, discloses a base fabric utilized in conjunction with a needled batt, the base fabric comprising interwoven core-wrapped yarns, the core yarns of which are effectively heat-infusible and the wrapping yarns effectively heat-fusible. Disclosed as the infusible yarns are aramid fibers, acrylic homopolymers, coated fiberglass, metalic fibers, and novoloid fibers. Disclosed as fusible materials are polyamide, polyester, polyolefin, and polyvinylchloride.
None of the prior art suggests the use of ionomer-coated nylon fibers as the cross-machine direction element of a woven mesh which forms the base layer of a batt-on-mesh papermakers' felt.
Thus, a need has continued to exist for a papermakers' press felt of the batt-on-mesh type which is smooth, has good drainage characteristics, and has improved abrasion resistance, batt retention, and dimensional stability.